极地研究

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Foreword

Mark Lester，Hu Hongqiao

2013, 24 (1-English): 0.

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The Super Dual Auroral Radar Network (SuperDARN): An overview of its development and science

Mark Lester

2013, 24 (1-English): 1-11. DOI: 10.3724/SP.J.1085.2013.00001

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The Super Dual Auroral Radar Network (SuperDARN) is a network of HF coherent scatter radars. At the end of 2012 there were 31 operational radars of which 22 were in the northern hemisphere and 9 in the southern hemisphere. The radars are operated by 17 different research groups from 11 different countries. In this paper we give an overview of the network and its development over the last twenty years, concentrating on the nature of the collaboration. We describe the data parameters that are available, radar operational modes, and the structure of the SuperDARN collaboration. A brief, “light touch” review is also given of the science achieved with the network. Finally we give a brief look to future science directions.

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Study of ionospheric disturbances during solar flare events using the SuperDARN Hokkaido radar

Daiki Watanabe，Nozomu Nishitani

2013, 24 (1-English): 12-18. DOI: 10.3724/SP.J.1085.2013.00012

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It is well known that many types of ionospheric disturbances occur during solar flare events. The sudden increase in total electron content (SITEC) has been studied for several decades, but total electron content (TEC) data do not provide information on the altitudinal distribution of electron density changes. Previous studies used HF Doppler system data to investigate the contributions of the D-region and F-region ionospheric electron density changes by examining the HF radio wave frequency dependence on the Doppler shift values. In this study we examined the dependence of the elevation angle of the Doppler shift of ground scatter echoes using the SuperDARN Hokkaido radar. We analyzed solar flare events from Dec 2006 to Mar 2012. A sudden fade-out of echoes was observed in almost all the events we analyzed, which was the result of the radio absorption associated with a significant increase in electron density within the D-region ionosphere. In addition, we discovered positive Doppler shifts just before the sudden fade-out of echoes. The Doppler shift is negatively correlated with the elevation angle of received radar waves. It indicates that variation of electron density in the D-region ionosphere is dominant during solar flare events. This result is consistent with a previous study. We also compared the irradiation by X-ray and extreme ultra violet rays observed by the GOES-14 and GOES-15 satellites, which generated Doppler shifts. A positive Doppler shift is consistent with a change of X-ray flux.

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Statistical characteristics of ionospheric backscatter observed by SuperDARN Zhongshan radar in Antarctica

HU Hongqiao，LIU Erxiao，LIU Ruiyuan，YANG Huigen，ZHANG Beichen

2013, 24 (1-English): 19-31. DOI: 10.3724/SP.J.1085.2013.00019

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Zhongshan HF radar, as one component of SuperDARN, has been established and in operation since April, 2010. Using data from the first two years of its operation, this paper investigates the radar’s performance, the diurnal and seasonal variations of ionospheric echoes, and their dependence on geomagnetic activity. Statistical studies show that the occurrence of echoes in different beams varies at different frequencies, which arises from the direction of the beam and the area over which the beam can achieve the orthogonality condition between the wave vector and the Earth’s magnetic field. The diurnal variation is obvious with double peak structures both in the occurrence rate and average power at 04–08 UT and 16–17 UT. The line-of-sight velocities are mainly positive on the dayside and negative on the nightside for Beam 0, which is the opposite of the trend for Beam 15. The spectral widths on the dayside are often higher than those on the nightside owing to the high energy particle precipitation in the cusp region. The seasonal variations are more obvious for those beams with larger numbers. The occurrence, the average power, the line-of-sight velocity, and the spectral widths are generally larger in the winter months than in the summer months. The influence of geomagnetic activity on radar echoes is significant. The peak echo occurrence appears on the dayside during geomagnetically quiet times, and shifts toward the nightside and exhibits an obvious decrease with increasing Kp. With increasing geomagnetic activity, the line-of-sight velocities increase, whereas the spectral widths decrease. The frequency dependence is investigated and it is found that in the operating frequency bands in 2010, 9–10 MHz is the most appropriate band for the SuperDARN Zhongshan radar.

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The substorm current wedge and midnight sector partial ring current near substorm onset: A synthesis based on a magnetotail magnetic field geometry model

George J Sofko，Kathryn A McWilliams，Chad R Bryant

2013, 24 (1-English): 32-41. DOI: 10.3724/SP.J.1085.2013.00032

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The Substorm Current Wedge (SCW) occurrence in the late growth and onset phases of substorms was proposed as the current system which disrupts cross-tail current by diverting it to the ionosphere. The closure current for the SCW originally was suggested to be the strong westward auroral electrojet (WEJ). However, the SCW-WEJ system has no viable generator current. Similarly, the asymmetric or Partial Ring Current (PRC) increases in strength during the growth phase, and is sometimes associated with an enhanced Region 2 field-aligned current (FAC) closing to the ionosphere, but specifics of that closure have been lacking. Here we present a unifying picture which includes the SCW post- and pre-midnight (AM and PM, respectively) currents and a generator current in the midnight portion of the PRC system, with these currents based upon a model of the nightside magnetotail magnetic geometry. That geometry consists of open north and south lobe regions surrounding a plasmasheet with two types of closed field line regions-stretched lines in the central part of the plasmasheet (SPS) and dipolar lines (DPS) between the low latitude boundary layer (LLBL) regions and the SPS. There is also an important plasmasheet transition region (TPS) in which the dipolar field near the plasmapause gradually transforms to stretched lines near the earthward edge of the SPS, and in which the midnight part of the PRC flows. We propose that our proposed near-onset current system consists of a central current which becomes
part of the midnight sector PRC and which is the generator, to which are linked two three-part current systems, one on the dawnside and one on the duskside. The three-part systems consist of up and down FACs closing as Pedersen currents in the ionosphere. These 3-part systems are not activated until near-onset is reached, because of a lack of ionospheric conductivity in the appropriate locations where the Pedersen current closure occurs. The initial downward FAC of the 3-part dawnside system and the final upward FAC of the 3-part duskside system correspond to the AM and PM current segments, respectively, of the originally proposed SCW.

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Northward-propagating nighttime medium-scale traveling ionospheric disturbances observed with SuperDARN Hokkaido HF radar and GEONET

Akimitsu Ichihara，Nozomu Nishitani，Tadahiko Ogawa，Takuya Tsugawa

2013, 24 (1-English): 42-49. DOI: 10.3724/SP.J.1085.2013.00042

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We report on the characteristics of nighttime medium-scale traveling ionospheric disturbances (MSTIDs) propagating northward observed with the SuperDARN Hokkaido HF radar, which has a field of view to the north of Japan, and occasionally with the GNSS Earth Observation NETwork (GEONET), which provides total electron content (TEC) data over Japan. From statistical analysis of MSTIDs observed with the Hokkaido radar during nighttime (1700–0700 LT) from January 2007 to July 2009, we find that these MSTIDs traveling northward, although rare in comparison with those traveling southwestward, have a relatively high occurrence rate after sunset and around midnight in May and August, which is partly consistent with the occurrence rate of MSTIDs over Japan observed with GEONET in 2002, when the MSTID event database is available. We also use the data from simultaneous observation of nightside MSTIDs by the Hokkaido radar and GEONET to find that when the HF radar observed northward-propagating MSTIDs, GEONET did not always observe such MSTIDs with the same propagation direction. Judging from this result and considering the HF radar field of view located to the north of the GEONET coverage area, we speculate that some physical parameters of the ionosphere/thermosphere over Japan differ from those to the north of Japan, which may result in the inconsistency of MSTID propagation direction. The present results provide new knowledge of MSTIDs propagating northward using the Hokkaido radar, whose field of view was not covered by GEONET.

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Assessing Doppler velocities of Rankin Inlet F-region echoes

Alexander V Koustov，Kale Colville，Robyn A D Fiori， Mohsen Ghezelbash

2013, 24 (1-English): 50-59. DOI: 10.3724/SP.J.1085.2013.00050

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Doppler velocities observed by the Rankin Inlet (RKN) PolarDARN radar are assessed with a focus on data in the beams oriented roughly along the magnetic meridian. Hourly scatter plots for every month are built. They are shown to vary widely, with median values showing very clear magnetic local time variation with maximum magnitude during pre-noon and pre-midnight hours. The histograms contain a significant amount of very small velocity data that dominates at farther ranges and during the daytime. Near noon data show generally antisunward flows but at large ranges/magnetic latitudes and very close to noon, sunward flows occur for periods of positive IMF Bz. The reverse flows are stronger during spring equinox. The velocity magnitude was found to depend linearly on the IMF Bz and interplanetary electric field. Velocities are often found to be smaller than those expected from the statistical convection model of Ruohoniemi and Greenwald –1996.

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Optical and SuperDARN radar observations of duskside shock aurora over Zhongshan Station

LIU Jianjun，HU Hongqiao，HAN Desheng，LIU Yonghua，ZHANG Qinghe，Akira S Yukimatu

2013, 24 (1-English): 60-68. DOI: 10.3724/SP.J.1085.2013.00060

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We present observations of a duskside shock aurora occurred on 21 April 2001 by the SuperDARN radar at Syowa Station and the all-sky camera at Zhongshan Station (ZHS) in Antarctica when the radar was operated in fast-scan mode covering the ZHS region. With the two independent data sets, we examine ionospheric plasma convection and aurora arising from a sudden impulse (SI) event associated with an interplanetary shock. During the transient shock compression, the aurora was quiescent without any optical emission at the preliminary impulse of the SI. About 7 min later, a new thin auroral arc with brighter emissions and a lifetime of ~14 min expanded westward from the region above ZHS during the main impulse of the SI. SuperDARN radar line-of-sight measurements showed periodical oscillation in the flow direction with ultra-low-frequency waves having a period of ~8 min during the shock compression. We suggest that downward field-aligned current during the preliminary impulse stage of the SI was the main driver of the first plasma flow reversal, and the subsequent new discrete auroral arc may be associated with field-aligned acceleration in the region of the main impulse related upward field-aligned currents. The ground magnetometer observations suggest that the oscillation of the ionospheric convection on the duskside was associated with field line resonance activity.

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An integrated analysis platform merging SuperDARN data within the THEMIS tool developed by ERG-Science Center (ERG-SC)

Tomoaki Hori，Nozomu Nishitani，Yoshizumi Miyoshi，Yukinaga Miyashita，Kanako Seki，Tomonori Segawa，Keisuke Hosokawa，Akira S Yukimatu，Yoshimasa Tanaka，Natsuo Sato，Manabu Kunitake，Tsutomu Nagatsuma

2013, 24 (1-English): 69-77. DOI: 10.3724/SP.J.1085.2013.00069

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The Energization and Radiation in Geospace (ERG) mission seeks to explore the dynamics of the radiation belts in the Earth’s inner magnetosphere with a space-borne probe (ERG satellite) in coordination with related ground observations and simulations/ modeling studies. For this mission, the Science Center of the ERG project (ERG-SC) will provide a useful data analysis platform based on the THEMIS Data Analysis software Suite (TDAS), which has been widely used by researchers in many conjunction studies of the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft and ground data. To import SuperDARN data to this highly useful platform, ERG-SC, in close collaboration with SuperDARN groups, developed the Common Data Format (CDF) design suitable for fitacf data and has prepared an open database of SuperDARN data archived in CDF. ERG-SC has also been developing programs written in Interactive Data Language (IDL) to load fitacf CDF files and to generate various kinds of plots−not only range-time-intensity-type plots but also two-dimensional map plots that can be superposed with other data, such as all-sky images of THEMIS-GBO and orbital footprints of various satellites. The CDF-TDAS scheme developed by ERG-SC will make it easier for researchers who are not familiar with SuperDARN data to access and analyze SuperDARN data and thereby facilitate collaborative studies with satellite data, such as the inner magnetosphere data provided by the ERG (Japan)−RBSP (USA)−THEMIS (USA) fleet.

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Call for papers for a special issue of AFoPS meeting 2012

2013, 24 (1-English): 78.

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